A detailed view on pin orientation when doing Base jumps, to avoid pin-locks. The described scenarios and pull orientations will most likely not happen in a slider up/ terminal [or skydiving] environment, but can/do happen on a slider down BASE jump. Thanks to Todd from Apex Base for pointing this out to me
Pull Direction
First, let’s define the pull directions and to which deployment position they fit (see above picture)
Up – happens in head high / standing position. Down – happens in head low / head down position Left – when jumper rolls to the right (right shoulder and hip down) Right – when jumper rolls to the left (left shoulder and hip down) Normal – when jumper is belly to earth
When flat and stable the bridle will pull in the ‘normal’ (pink) direction.
Pin Orientation: Happy or Sad
Second, assign the following names to the pin orientations when looking at the rig; happy and sad.
Since I had a hard time wrapping my head around the whole thing I made a few pictures to make sure everyone knows what I’m talking about. This picture shows the pin and bridle on a packed rig as if you could look through the bridle.
Scenario 1: Sad Pin
The pin is ‘sad’ and the retainer tab sits on the bottom of the eye of the pin like in the pictures above. When pulling the bridle straight up and away from the container, therefore force is applied in ‘normal’ pull direction the pin will first rotate in the loop and then slide out of the loop.
This works like a charm and required force for both steps to happen should be rather low, of course depending on loop tension. (The term ‘pin tension’ is a little misleading in this context because it normally addresses the force required to pull the pin… since this is the variable part here I use ‘loop tension’ when I really mean the tension of the loop.)
The force required to pull the bottom pin of my slider down rig (the one in the pictures) in this scenario is approximately 0.25 kg (~0.5 lbs), the pins were fully set.
Scenario 2: Happy Pin
The pin is ‘happy’ and retainer tab sits on the bottom of the eye of the pin like in the pictures at the top of this post. When pulling the bridle in ‘normal’ direction, the pin cannot rotate in the loop like in scenario 1 because its tip tries to dig into the container, levering against the force applied by the bridle on the eye-end of the pin. So the pin has to turn around the loop before it can start sliding out of it.
At high airspeeds this would likely correct itself. At low airspeeds it could be fatal.
The force required to pull the pin increases significantly compared to scenario 1, the pull force measured on the same rig as above reached up to 3 kg (~6.5 lbs), therefore around the ten-fold of the first measurements. (Again the pins were fully set.)
At higher airspeeds this is going to be less of an issue due to the increased pull force of the pilot chute (and the changing angle of the applied force as soon as you start moving forward, ie, tracking or wing suiting)… but can become a problem if you’re doing short delays where you don’t want to have any hesitations in the opening process.
Scenario 3: Straight
The pin is pointing straight up. In this case the pin will turn in the loop to either, a ‘sad’, or a ‘happy’ orientation, whichever is closer. From there, scenario 1 or 2 applies.
Summary
Pin orientation matters! Do a pincheck before you jump, have the pins in a ‘sad’ orientation, and if you’re going for a short delay, prime the pins, and leave your pin protector flap open.
More information on this and related topics by Hirschi (Thomas Hirsch) can be found at Watch Thy Bridle.
Disclaimer!
It goes without saying that you cannot learn to Base jump or pack on the internet. This article is for background only.
